The invention relates to an exhaust tract for an internal combustion engine of a motor vehicle having a first exhaust gas line, which conducts exhaust gases from the internal combustion engine to an exhaust-gas treatment device, and a second exhaust gas line, which forms a bypass line bypassing the exhaust-gas treatment device.
The action of three-way catalytic converters known from the prior art is not sufficient during the lean operation mode of a spark-ignition internal combustion engine.
The object of the present invention is to provide an exhaust tract, in which a sufficient treatment of the exhaust gas is ensured even in the lean operating mode of an internal combustion engine.
This object is achieved by an exhaust tract wherein at least one first valve and one second valve are disposed in series in the bypass line. An exhaust line is provided between the first valve and the second valve to reduce the pressure between the first and second valves. The pressure upstream of the second valve and the pressure downstream of the second valve or the ambient pressure of the motor vehicle, are determined, and negative pressure is applied to the exhaust line such that an exhaust gas flow via the second valve to the outside into the environment of the motor vehicle is prevented. Advantageous embodiments of the invention are described herein.
Based on an exhaust tract of a motor vehicle including a first exhaust gas line, which conducts the exhaust gases from the internal combustion engine to an exhaust-gas treatment device, and a second exhaust gas line, which forms a bypass line bypassing the exhaust-gas treatment device, at least one first valve and one second valve are disposed in series in the bypass line. An exhaust line is provided between the first valve and the second valve to reduce the pressure between the first and second valves. The pressure upstream of the second valve and the pressure downstream of the second valve, or the ambient pressure of the motor vehicle, are determined, and negative pressure is applied to the exhaust line such that an exhaust gas flow via the second valve to the outside into the environment of the motor vehicle is prevented.
It can thus be ensured that only sufficiently treated exhaust gas leaves the motor vehicle. This is achieved, in particular, by the two valves disposed in series and the exhaust line provided between them for exhausting the exhaust gas present directly upstream of the second valve.
In one embodiment of the invention, the negative pressure in the exhaust line increases in the case of a rise in the differential pressure between the pressure upstream of the second valve and the pressure downstream of the second valve, or the ambient pressure. It is not always possible to ensure that valves or exhaust flaps disposed in the hot exhaust gas always close to a sufficient and/or same degree even after a long period of use. These negative basic conditions are confronted most effectively according to the invention by suitably adjusting the negative pressure or the degree of exhaustion by the exhaust line.
In one embodiment of the invention, the closing pressure of at least the second valve increases in the case of a rise in the differential pressure between the pressure upstream of the second valve and the pressure downstream of the second valve, or the ambient pressure. This supplementary or alternative measure can also prevent the discharge of insufficiently treated exhaust gas.
In one embodiment of the invention, when a predefined differential pressure between the pressure upstream of the second valve and the pressure downstream of the second valve, or the ambient pressure, is below a certain level (falls short), a fault message is generated and stored for diagnostic purposes. This fault can be indicated to the driver visually or acoustically so that repairs may be carried out in the short term. Furthermore, e.g., within the scope of a fault diagnosis at a regular vehicle service, the workshop receives an indication of the presence of the fault by way of the stored fault message, unless this fault has been repaired and the corresponding entry in the fault memory has already been deleted.
In one embodiment of the invention, in the case of a rise in the differential pressure between the pressure upstream of the second valve and the pressure downstream of the second valve, or the ambient pressure, the first valve is changed in the direction of the open position and the exhaust gas flow through the exhaust line is thus increased, and preferably the differential pressure is also reduced or largely held constant. This is a further measure which, alternately or additionally, can ensure the discharge of only sufficiently treated exhaust gas.
In an additional embodiment of the invention, the first valve and the second valve are actuated in a largely parallel manner in the case of a bypass of the exhaust-gas treatment device. This measure can reduce the mechanical or other expenditures incurred for ensuring the tightest possible closure of the valves and the exhaust flaps, e.g., by an arrangement of rods joining both valves for actuation.
In one embodiment of the invention, the exhaust line is connected to the internal combustion engine, and the intake of the internal combustion engine or a vacuum pump operated by the internal combustion engine generates a negative pressure in the exhaust line. The negative pressure required according to the invention can thus be created between the two valves with less expenditure.
In a preferred embodiment of the invention, the exhaust-gas treatment device is a nitrogen-oxide storage catalytic converter. This catalytic converter enables sufficient treatment of the exhaust gases of a gasoline engine in the lean operating mode if the exhaust-gas treatment by the conventional three-way catalytic converter is not sufficient.
In an additional preferred embodiment of the invention, the first valve and the second valve are closed so that the exhaust gases are largely conducted to the outside via the exhaust-gas treatment device, and a small part of the exhaust gases is returned via the exhaust line into the internal combustion engine when the internal combustion engine is operated in the lean operating mode.
In one embodiment of the invention, the first valve and the second valve are open and a third valve, provided upstream of the exhaust-gas treatment device, is closed when the internal combustion engine is operated outside the lean operation mode. The exhaust gases are then conducted to the outside via the bypass line. An additional valve is preferably disposed downstream of the exhaust-gas treatment device in order to prevent the harmful penetration of exhaust gases into the exhaust-gas treatment device via the outlet of the same.
In one embodiment of the invention, a fourth valve is provided in the exhaust line. The negative pressure in the exhaust line is preset with the aid of the position of the fourth valve.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.